Corrosion resistant electrodes for iontophoretic transdermal delivery devices and methods of use

ABSTRACT

Embodiments of the invention provide electrode assemblies and associated methods for the iontophoretic transdermal delivery of therapeutic agents. Many embodiments provide a corrosion resistant electrode for the iontophoretic transdermal delivery of various therapeutic agents. Such embodiments allow for the iontophoretic transdermal delivery of therapeutic agents such as iron compounds for prolonged periods without any substantial corrosion of the electrode, impedance increases or discoloration or irritation of the skin. Embodiments of the invention are particularly useful for the long term treatment of various chronic medical conditions such as iron deficient anemia.

RELATIONSHIP TO OTHER APPLICATIONS

This application claims the benefit of priority to Provisional U.S.Patent Application No. 61/221,010, entitled “Corrosion ResistantElectrodes for Iontophoretic Transdermal Delivery Devices”, filed Jun.26, 2009; the aforementioned priority application being herebyincorporated by reference for all purposes.

This application is also related to concurrently filed applicationentitled “Corrosion Resistant Electrodes for Iontophoretic TransdermalDelivery Devices and Methods of Use.”, which is being herebyincorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

Embodiments described herein relate to electrode assemblies foriontophoretic transdermal delivery devices used for the delivery ofvarious therapeutic agents. More specifically, embodiments describedherein relate to conductive materials for electrode assemblies foriontophoretic transdermal delivery devices.

BACKGROUND

Iontophoresis is a non-invasive method of propelling high concentrationsof a charged substance, known herein as the active agent, transdermallyby repulsive electromotive force using a small electrical charge. Theactive agent can include a drug or other therapeutic agent. The chargeis applied by an electrical power source to an active electrode assemblyplaced on the skin which contains a similarly charged active agent and asolvent in which it is dissolved. Current flows from the electrodeassembly through the skin and then returns by means of a return orcounter electrode assembly also placed on the skin. A positively chargedelectrode assembly, termed the anode will repel a positively chargedactive agent, or anion, into the skin, while a negatively chargedelectrode assembly, termed the cathode, will repel a negatively chargedactive agent, known as a cation into the skin.

Over time, metal electrodes used in iontophoretic transdermal patchesmay become corroded due to electrochemical corrosion of the metal duringcurrent flow through the electrode. Corrosion can increase theelectrical impedance of the patch, decreasing the current delivered fromthat patch to the skin with a resulting decrease in the delivery rate oftherapeutic agents from the patch. There is a need for electrochemicallycorrosion resistant electrode materials used in iontophoretictransdermal patches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral view showing an embodiment of a corrosion resistantelectrode assembly for an iontophoretic transdermal delivery of atherapeutic agent.

FIG. 2 is a top down view of the embodiment of FIG. 1.

FIG. 3 is a prophetic plot showing the impedance for an embodiment of acorrosion resistant electrode during a period of current flow throughthe electrode and transdermal/iontophoretic delivery of a therapeuticagent.

FIG. 4 is a lateral view showing an alternative embodiment of acorrosion resistant electrode comprising carbon impregnated fibers.

FIGS. 5 a and 5 b are top views showing different embodiments for theshape of the electrode. FIG. 5 a shows an embodiment having asubstantially disc shape. FIG. 5 b shows an embodiment having asubstantially oval shape.

FIGS. 6 a and 6 b are lateral views showing different embodiments forthe diameter of the electrode relative to the diameter of the poroustissue contacting layer. FIG. 6 a shows an embodiment where the diameterof the electrode is smaller than the diameter of the tissue contactinglayer. FIG. 6 b shows an embodiment where the electrode and the porouslayer have substantially the same diameter.

FIGS. 7 a-7 d are lateral views showing different embodiments for thecontour of the edges of the electrode; FIG. 7 a shows an embodimenthaving a substantially squared edge; FIG. 7 b shows an embodiment havinga substantially rounded edge; FIG. 7 c shows an embodiment having atleast a partially tapered edge; and FIG. 7 d shows an embodiment of theelectrode having a concave contour.

FIG. 8 is a lateral view showing an embodiment of a corrosion resistantelectrode assembly including a reservoir for therapeutic agent where theelectrode is positioned adjacent the reservoir.

FIG. 9 is a lateral view showing an embodiment of a corrosion resistantelectrode assembly including a reservoir and a self sealing port forfilling the reservoir with a therapeutic agent solution.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein provide electrode assemblies for theiontophoretic transdermal delivery of therapeutic agents. Manyembodiments provide a corrosion resistant electrode for the transdermaldelivery of therapeutic agents. Such embodiments can be utilized for thedelivery of a number of therapeutic agents including the delivery ofiron containing compounds for the treatment of iron deficiency anemiaand other iron deficiency diseases and conditions.

One embodiment provides a corrosion resistant electrode assembly for theiontophoretic transdermal delivery of a therapeutic agent, the electrodeassembly comprising a conformable layer conformable to a contour of askin surface and having a tissue contacting side and non-tissuecontacting side; an electrical connector positioned on the non-tissuecontacting side of the conformable layer, an electrode operativelycoupled to the connector; and a tissue contacting porous layerpositioned on the tissue contacting side of the conformable layer andoperatively coupled to the electrode. The electrical connector isconfigured to be operatively coupled to an electrical power source suchas an alkaline or lithium battery or other portable power source. Theelectrode is at least partially disposed in the porous layer.

In some embodiments, the electrode comprises a graphite or otherelectrochemically un-reactive material such that the electrode does notsubstantially corrode when current flows through the electrode from thepower source during periods of iontophoretic transdermal delivery of thetherapeutic agent.

Additionally, some embodiments provide that the electrode is structuredto have sufficient corrosion resistance such that the impedance throughthe electrode does not substantially increase during periods of currentflow through the electrode, for example, for periods of 12 to 96 hoursor longer. Additionally, the electrode comprises a material which issufficiently corrosion resistant and chemically inert such that it willnot cause any appreciable discoloration or irritation of the skin fromany corrosion that may occur.

In preferred embodiments, the electrode comprises a flexible compressedgraphite material. Other graphites or organic compositions such aspyrolytic graphite are also considered. In alternative embodiments, theelectrode can comprise a carbon impregnated polymer such as rubber oreven polymer fibers such as cotton, polyesters, polysulphone or otherpolymeric fibers known in the art.

Typically, the electrode will have a thin disc shape with a preferredthickness of about 0.5 mm to about 2 mm. However, other shapes andthicknesses are also contemplated such as an oval shape. For disc andother shaped embodiments, the edges of the electrode can be square,rounded with a selected radius or even tapered partially or fully tominimize any electrical edge effects (e.g., currentconcentrations/increased current density at the electrode edges andresulting ohmic or other heating). The entire disc can also have aconcave/dogbone contour to minimize edge effects by having the electrodehave a larger thickness on the edges. In various embodiments, theelectrode can be sized such that it has substantially the same surfacearea (e.g., diameter for disc shaped embodiments) as the underlyingtissue contacting porous layer or it may have a smaller surface area,for example, 50% or 25% of the surface area of the porous layer. Nomatter what the size, the electrode can be centered above the tissuecontacting porous layer, such that it is concentric with respect to theporous layer, though eccentric configurations are also contemplated.

In some embodiments, the electrode can also be sufficiently flexible sothat it can bend and flex with the entire electrode assembly in order toconform to the contour of the skin surface. However, stiffer embodimentsare also contemplated. Also, typically the electrode will be placed indirect contact with the tissue contacting porous layer and positioneddirectly above it relative to the non-tissue contacting side of theconformable layer. However, the electrode may also be operativelyelectrically coupled to the porous layer through an intermediaryconductive material.

The tissue contacting porous layer is operatively coupled to theelectrode such that the current from the electrode flows into the porouslayer. In many embodiments, the porous layer will be in direct contactwith the electrode, though use of an intermediary conductor is alsocontemplated to electrically couple the two structures. The porous layercan comprise compressed cotton or other fiber such as a polyester fiberor polysulphone and may be woven. The porous layer may have asufficiently tight weave or other configuration such that it can captureany pieces of electrode material that break off from the electrode dueto small amounts of corrosion during periods of current flow through theelectrode.

In various embodiments, the electrode assembly can also include areservoir for a solution containing the therapeutic agent. Typically,the electrode will be placed in direct contact with the reservoir,however, it may also be offset from the reservoir and operativelyelectrically coupled to it through an intermediary conductor. Inembodiments having a reservoir, the electrode material comprisesgraphite or other material sufficiently resistant to electrochemicalcorrosion by an aqueous based therapeutic agent solution.

Still further, many embodiments include provide corrosion resistantelectrodes and corrosion resistant electrode assemblies for use withiontophoretic transdermal delivery devices, such as various skinconformable patches for the iontophoretic transdermal delivery ofvarious therapeutic agents (also described herein as the active agent).Such agents can include, for example, insulin, antibiotics, analgesics,chemotherapeutics and iron containing compounds for the treatment ofanemia. Suitable iron compounds can comprise ionic iron in the form offerrous (Fe²⁺) or ferric (Fe³⁺) iron. The ionic iron can comprise aniron salt, a ferrous salt, a ferric salt, ferric pyrophosphate, ferrouschloride or a combination thereof. Still other iron containing compoundsknown in the anemia treatment arts are also contemplated.

In specific embodiments, the active agent can comprise a sufficientamount of elemental iron for the treatment of iron deficiency anemia.The amount of elemental iron can be sufficient to provide between 1 to100 mg of elemental iron to the patient a day for a period of days oreven weeks. Further description on suitable iron compounds for thetreatment of iron deficient anemia and like conditions may be found inU.S. patent application Ser. No. 12/459,862, filed Jul. 7, 2009 andentitled “Method For Transdermal Iontophoretic Delivery Of ChelatedAgents”, which is fully incorporated by reference herein for allpurposes.

Referring now to FIGS. 1-2, an embodiment of a corrosion resistantelectrode assembly 10 for use with a iontophoretic transdermal deliverydevice 5 such as a patch device 5, comprises a conformable layer 20, anelectrical connector 30, an electrode 40 and a porous tissue contactinglayer 50. Conformable layer 20 is conformable to the contour of a skinsurface and has a skin contacting side 21 and non-skin contacting side22. The conformable layer 20 can comprise various elastomeric polymersknown in the art such as polyurethane or silicone and has sufficientflexibility to not only conform to a contour of the skin surface butalso to bend and flex with movement of the skin.

Electrical connector 30, hereafter connector 30, is typically positionedon the non-tissue contacting side 22 of conformable layer 20 andcomprises any number of standard electrical connectors such as variousnipple connectors known in the medical instrument and electronics arts.The connector 30 is also directly or otherwise “electricallyoperatively” (hereinafter “operatively”) coupled to electrode 40. It isalso configured to be coupled to an electrical power source 60 which maycomprise one or more portable batteries 65 such as alkaline, lithium,lithium ion or other battery chemistry known in the art.

Electrode 40 includes an electrochemically corrosion resistant material(hereinafter “corrosion resistance”) such that the electrode 40 does notundergo appreciable amounts of electrochemical corrosion (e.g., byoxidation or other related reactions) resulting from current flowthrough the electrode during iontophoretic transdermal delivery of thetherapeutic agent or from any other current flow or electrical potentialapplied to the electrode.

The corrosion resistance of electrode 40 is also configured such thatthe conductive surface area 40SAC of the electrode is substantiallypreserved during periods of iontophoretic transdermal drug delivery. Thepreservation of surface area 40SAC in turn prevents any substantialincrease in impedance of electrode 40. In specific embodiments,electrode 40 is configured to resist corrosion and maintain asubstantially constant impedance or otherwise resist any appreciableimpedance increases for currents in the range of 0.1 ma to 10 ma andvoltage from 1 v to 100 v for periods of current flow of 12, 24, 48, 72or 96 hours or longer as is shown in FIG. 3.

Among other benefits, embodiments of a corrosion resistant electrode 40provide several benefits for iontophoretic transdermal delivery ofvarious therapeutic agents such as iron containing compounds, insulin,etc. These can include allowing the maintenance of a substantiallyconstant voltage applied to an iontophoretic transdermal patch deviceduring a period of iontophoretic transdermal delivery and/or keeping thevoltage below a desired threshold. The applied voltage is used iniontophoretic transdermal delivery to provide the electromotive drivingforce for propelling charged therapeutic agents, such as ionic ironcompounds, into the skin. If the impedance of the electrode increases asa result of corrosion, larger voltages may be required. Maintaining asubstantially constant voltage during a period of iontophoreticdelivery, or keeping it below a selected threshold, serves to increasebattery life, (for embodiments of battery-powered iontophoretic patchdevices) and reduces the likelihood of pain perception of the user bykeeping the voltage below a pain threshold.

In particular embodiments, the voltage can be kept below a threshold ofabout 100 volts and still more preferably below about 40 volts.Additionally, having a corrosion resistant electrode can also allow thecurrent density associated with electrode 40 and/or electrode assembly10 to be kept below a threshold (for example, the threshold for causingpain to the patient). This is due to the fact that the conductivesurface area 40SAC of the electrode 40 remains substantially intactduring the course of current delivery. In particular embodiments, thecurrent density threshold associated with electrode 40 and/or electrodeassembly 10 can be kept below about 1.0 ma/cm², more preferably belowabout 0.8 ma/cm², still more preferably below about 0.5 ma/cm² and stillmore preferably below about 0.2 ma/cm². Still lower values for thecurrent density are contemplated.

As an addition or alternative, electrode 40 comprises a material whichis sufficiently corrosion resistant and chemically inert such that itwill not cause any appreciable discoloration or irritation/inflammationof the skin or other foreign body response from any amount of corrosionthat may occur (e.g., resulting in contact or penetration of theelectrode material into the skin). In various embodiments, these resultscan be achieved by the selection of a carbon-based electrode materialsuch as graphite, which is both corrosion resistant and relativelychemically inert to body tissue.

In many embodiments, electrode 40 comprises a conductive graphitematerial. Graphite is a layered carbon material in which the layerscomprise hexagonal lattices of carbon atoms. Graphite can conductelectricity due to extensive electron dislocations within each layer. Inpreferred embodiments, the electrode comprises a flexible compressedgraphite material such as a flexible graphite sheet which can befabricated using a calendaring or other compression process known in theart. In such embodiments, the graphite material can have sufficientflexibility to allow the electrode 40 to flex along with the rest ofelectrode assembly 10 so as to conform to the contour of the skin at aselected application site. An example of a suitable graphite includesgrade INTRS-PGS394 having a thickness of about 0.06″ available from theGraphiteStore.com (Buffalo Grove, Ill.).

Embodiments include use of other graphites such as pyrolytic graphite.Pyrolytic graphite is a unique form of graphite manufactured bydecomposition of a hydrocarbon gas at very high temperature in a vacuumfurnace. The result is an ultra-pure product which is near theoreticaldensity and extremely anisotropic. Specific embodiments of pyrolyticgraphite electrode 40 can be configured to allow for the electricalconduction through the electrode, but provide for thermal insulation inone or more directions.

In alternative embodiments, electrode 40 can comprise a graphite/carbonimpregnated including polymer fibers such as cotton, polyesters,polysulphone other polymeric fibers known in the art. An example of acarbon/graphite impregnated fiber is shown in the embodiment of FIG. 4.In this embodiment, particles 43 of graphite powder are bound to fibers44. In other alternative embodiments, a corrosion resistant electrode 40can comprise a carbon impregnated rubber or other carbon impregnatedsolid polymer, which can comprise various resilient polymers known inthe art, allowing the electrode to bend and flex to conform to thecontour of the skin surface. In use, such embodiments allow current tobe delivered from an electrode assembly (including at least a portion ofthe electrode) in a bent position while preventing or minimizing anyimpedance rise in the electrode assembly due to corrosion of theelectrode.

Still other alternative embodiments of a corrosion resistant electrode40 can comprise carbon fibers (either turbostratic or graphitic carbon,or with a hybrid structure having both graphitic and turbostraticparts). In such embodiments, a disc or other shaped electrode 40, can becut from a carbon fiber rod. In still other alternative embodiments, acorrosion resistant electrode can comprise carbon black material, forexample, compressed carbon black powder, or polymer, such as polymerfibers impregnated with carbon black.

Typically, the electrode 40 will have a thin disc shape 41 as is shownin the embodiments of FIGS. 2 and 5 a. However, other shapes 40 s arealso contemplated, such as an oval shape 40 o as is shown in theembodiment of FIG. 5 b which can be use in an oval shaped patch device5. The thickness 40 t of the electrode 40 is selected to allow for bothflexibility (e.g., to conform to the contour of the skin surface) andcorrosion resistance of the electrode. In preferred embodiments,electrode 40 has a thickness 40 t in the range of about 0.5 to about 2mm. Other ranges of thickness are also contemplated, for example, about2 mm to about 4 mm. Increased thickness's can be selected where morestiffness in electrode 40 is desired.

Typically, electrode 40 will be placed in direct contact with the tissuecontacting porous layer 50 and positioned directly above it relative tothe non-tissue contacting side 22 of the conformable layer 20. Inalternative embodiments, it may also be operatively electrically coupledto the porous layer through an intermediary conductive material (notshown). In still other alternative embodiments, portions of electrode 40can be wrapped around porous layer 50 so that portions of the electrodeare on the top and the sides of the porous layer 50.

According to some embodiments, the electrode 40 can be positioned invarious locations in or on conformable layer 20. In preferredembodiments, electrode 40 is fully disposed within layer 20, so that itis electrically insulated, but also may have all or a portion positionedon the tissue 21 or non-tissue contacting sides 22 of layer 20. In theseembodiments, the electrode 40 has an insulated coating (not shown) forthose portions which are exposed. In some embodiments, all or a portionof electrode 40 can be placed in close proximity to the tissuecontacting side 21, (e.g., within 0.01″ or less).

Electrode 40 can have a variety of sizes depending one or more on theamount of conductive surface area 40SAC desired, as well as the size ofthe underlying porous layer 50 and the various electrical parameters(e.g., current voltage, etc.) used for the iontophoretic transdermaldelivery of therapeutic agent 85. In various embodiments, electrode 40can be sized such that it has substantially the same surface area 40SA(and diameter 40D for disc shaped embodiments of the electrode) as thesurface area 50SA (and diameter 50D for disc shape embodiments of theporous layer) for the underlying tissue contacting porous layer 50, asis shown in the embodiment of FIG. 6 b. Alternatively, it may have asmaller surface area as is shown in the embodiment of FIG. 6 a, forexample, 50% to 25% of the surface area 50SA of porous layer 50. Nomatter what the size, the electrode is centered above the tissuecontacting porous layer 50, such that it is concentric with respect tothe porous layer, though eccentric configurations are also contemplated.

Referring now to FIGS. 7 a-7 d, in various embodiments, the edges 40 eof electrode 40 can also have a selectable shape 40 es depending uponone or more of the size of the electrode and various electricalparameters (e.g., current, voltage, etc.) used for a particulariontophoretic transdermal patch 5. In particular embodiments, the shape40 es of edge 40 e can be square (shown in the embodiment of FIG. 7 a)or rounded with a selected radius (shown in the embodiment of FIG. 7 b)to minimize any edge effects or even tapered (shown in the embodiment ofFIG. 7 c). For disc shaped embodiments of electrode 40, the entireelectrode can have a concave/dogbone contour 40 c to minimize edgeeffects by having the electrode have a larger thickness 40 t on theedges 40 e (as is shown in the embodiment of FIG. 7 d).

Referring back to FIGS. 1-6, tissue contacting porous layer 50 isoperatively coupled to the electrode 40 such that the current from theelectrode flows into the porous layer. In many embodiments the porouslayer 50 is in direct contact with electrode 40 as is shown in theembodiment of FIG. 1. However, in other embodiments, such as in theembodiment of FIG. 8, the use of an intermediary conductor, (in thiscase, a conductive therapeutic agent solution) is also contemplated toelectrically couple the two structures. In various embodiments, porouslayer 50 can comprise various fibers such as a polyester (e.g., PET) orpolysulphone fiber and may be compressed and/or woven. Various polymericfoams may also be used. In preferred embodiments, the porous layercomprises compressed cotton. In one embodiment, the porous layer 50 hasa sufficiently tight weave or other related property (e.g., porosity)such that it can capture any piece of electrode material that breaks offfrom electrode 40 due to small amounts of corrosion during periods ofcurrent flow through the electrode. In particular embodiments, theporous materials may also include various chemical functional groups orcoatings selected to bind the graphite or other electrode material toprovide an additional means for preventing the corrosive breakdown ofelectrode 40 and/or capturing pieces of corroded electrode 40 beforethey break off.

Referring now to FIGS. 8-9, in various embodiments, electrode assembly10 can also include a reservoir 70 for a solution 80 containing atherapeutic agent 85 as is shown in the embodiments of FIGS. 8 and 9.Typically, in such embodiments, electrode 40 will be placed in directcontact with reservoir 70; however, it may also be offset from reservoir70 a selected distance and operatively, electrically coupled to itthrough an intermediary conductor (not shown). In embodiments having areservoir 70, the electrode material comprises graphite or othermaterial sufficiently resistant to electrochemical corrosion by anaqueous based therapeutic agent solution. As an addition or alternativeto reservoir 70, solution 80 and/or therapeutic agent 85 by itself mayalso be disposed in other locations within assembly 10. It may forexample, be disposed within porous layer 50 (e.g., by injecting solution80 into the porous layer prior to use, or the therapeutic agent can becoated onto the fibers of porous layer 50 with solution 80 subsequentlyadded so that agent then dissolves in the solution). Still otherembodiments, contemplate operably associating therapeutic agent solution80 to assembly 10 by an external source, for example, an externalreservoir (not shown) or other that is fluidically coupled to porouslayer 50 or other portion of assembly 10.

In embodiments of electrode assembly 10 having a reservoir 70, theelectrode assembly 10 can also include a self sealing port 12fluidically coupled to reservoir 70 for filling the reservoir withtherapeutic agent 80. The self sealing port 12 can comprise a silicone,or other elastomeric material, and allows the electrode assembly 10 tobe filled with therapeutic solution 80 using a syringe and/or a mixingbottle with pointed tip and to do so using sterile technique. Typically,port 12 will include a channel 13 fluidically coupling the port 12 tothe reservoir 70. In these and related embodiments, electrode 40 issized and positioned within layer 20 such that a needle or other portpenetrating tip used to do the injection, will not make contact withelectrode 40. Also, an electrically insulating layer or barrier 14 canbe positioned between port 12 and/or channel 13 and electrode 40 tominimize the likelihood of any electrical conduction between port 12and/or channel 13 and the electrode. Barrier 14 can comprise variousinsulating polymers and other materials known in the art and can alsohave sufficient hardness to reduce the likelihood of penetration ofelectrode 40 by the needle tip or other port penetrating tip.

CONCLUSION

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to limit the invention to the precise forms disclosed. Manymodifications, variations and refinements will be apparent topractitioners skilled in the art. For example, the iontophoreticelectrode can be modified in material composition, size, and shape,depending upon one or more factors such as the type and amount oftherapeutic agent; the tissue site, for the application of transdermalpatch or other transdermal delivery device 5, and the projected weartime and conditions (e.g., hours vs. days, temperature, humidity, etc).

Elements, characteristics, or acts from one embodiment can be readilyrecombined or substituted with one or more elements, characteristics oracts from other embodiments to form numerous additional embodimentswithin the scope of the invention. Moreover, elements that are shown ordescribed as being combined with other elements, can, in variousembodiments, exist as standalone elements. Hence, the scope of thepresent invention is not limited to the specifics of the describedembodiments, but is instead limited solely by the appended claims.

What is claimed is:
 1. A corrosion resistant electrode assembly for theiontophoretic transdermal delivery of a therapeutic agent, the assemblycomprising: a conformable layer conformable to a contour of a skinsurface, the conformable layer having a tissue contacting side andnon-tissue contacting side; an electrical connector positioned on thenon-tissue contacting side of the conformable layer, the connectorconfigured to be coupled to an electrical power source; a tissuecontacting porous layer positioned on the tissue contacting side of theconformable layer and operatively coupled to an electrode; wherein theelectrode is operatively coupled to the connector and at least partiallydisposed in the porous layer, the electrode comprising anelectrochemically un-reactive material such that the electrode does notsubstantially corrode when current flows through the electrode from thepower source.
 2. The electrode assembly of claim 1, wherein theelectrode is in direct contact with the tissue contacting porous layer.3. The electrode assembly of claim 2, wherein the electrode ispositioned directly above the tissue contacting porous layer relative tothe non-tissue contacting side of the conformable layer.
 4. Theelectrode assembly of claim 1, wherein the electrode has a substantialdisc shape.
 5. The electrode assembly of claim 1, wherein the electrodehas a thickness and flexibility allowing the electrode to bend and flexto conform to a contour of the skin surface while maintaining itsanti-corrosion properties.
 6. The electrode assembly of claim 1, whereinthe electrode has radiused edges configured to minimize electrical edgeeffects.
 7. The electrode assembly of claim 1, wherein the electrodematerial comprises graphite carbon.
 8. The electrode assembly of claim7, wherein the graphite carbon is solid graphite or compressed graphite.9. The electrode assembly of claim 7, wherein the electrode has athickness from about 0.5 mm to about 1 mm.
 10. The electrode assembly ofclaim 1, wherein the electrode material comprises pyrolytic carbon. 11.The electrode assembly of claim 1, wherein the electrode materialcomprises carbon impregnated polymer.
 12. The electrode assembly ofclaim 11, wherein the polymer is a rubber, polymer, polymer fiber,polyester fiber, or polysulphone fiber.
 13. The electrode assembly ofclaim 1, wherein the electrode is configured such that an electricalimpedance of the electrode does not substantially increase duringperiods of current flow through the electrode to the skin surface. 14.The electrode assembly of claim 13, wherein the periods of current floware up to about 24 hours.
 15. The electrode assembly of claim 13,wherein the periods of current flow are up to about 48 hours.
 16. Theelectrode assembly of claim 13, wherein the periods of current flow areup to about 96 hours.
 17. The electrode assembly of claim 1, wherein theelectrode is sufficiently electrochemically un-reactive such that theelectrode does not cause any substantial discoloration of the skinsurface during a period of current flow through the electrode to theskin surface to deliver the therapeutic agent into the skin surface. 18.The electrode assembly of claim 1, wherein the electrode is sufficientlyelectrochemically un-reactive such that the electrode does not cause anyirritation of the skin surface during a period of current flow throughthe electrode to the skin surface to deliver the therapeutic agent intothe skin surface.
 19. The electrode assembly of claim 1, wherein theelectrode material comprises carbon or carbon impregnated fibers, thetissue contacting porous layer configured to substantially capture anycarbon material dislodged from the electrode during periods of currentflow through the electrode.
 20. The electrode assembly of claim 19,wherein the tissue contacting porous layer comprises cotton.
 21. Theelectrode assembly of claim 1, wherein the tissue contacting porouslayer comprises foam or cotton.
 22. The electrode assembly of claim 1,further comprising a reservoir for the therapeutic agent, wherein thereservoir is at least partially disposed in the tissue contacting layerand fluidically coupled to the tissue contacting porous layer.
 23. Theelectrode assembly of claim 22, wherein the electrode is positioneddirectly above the reservoir relative to the non-tissue contacting sideof the conformable layer.
 24. The electrode assembly of claim 1, furthercomprising a therapeutic agent operatively associated with the electrodeassembly.
 25. The electrode assembly of claim 24, wherein thetherapeutic agent comprises an ionic iron compound.
 26. The electrodeassembly of claim 24, wherein the therapeutic agent is disposed withinthe electrode assembly.
 27. A system for the iontophoretic transdermaldelivery of a therapeutic agent, the system comprising: the electrodeassembly of claim 1; and an electrical power source operatively coupledto the electrode assembly.